With the quickly developed electronic industrial field, the currently available electronic elements have constantly upgraded performance and accordingly, very fast computing speed. As a result, a large amount of heat is generated by the electronic elements during the high-speed operation thereof. The large amount of heat must be timely removed from the electronic elements to protect the electronic elements against lowered operational performance or even burnout. Therefore, a small-size centrifugal fan is usually utilized in the limited space of an electronic product for removing heat therefrom. The centrifugal fan mainly includes a frame, a hub, and a plurality of blades externally spaced along the hub. The frame defines at an upper and a lower side with an air-in opening each, and at one lateral side with an air-out opening. When the centrifugal fan operates, the blades rotate to cause ambient air to flow. Air axially flows into the frame via the upper and lower air-in openings is guided by the blades to flow in a radial direction of the hub and out of the centrifugal fan via the air-out opening.
To produce higher air pressure and more air flows, fan manufacturers have made efforts to change the shape of the blades. However, the effects of increased pressure and air flow that can be obtained via modification of blade shapes are limited and fail to satisfy general users' demands. Further, since the centrifugal fan has a relatively small frame, which also limits the possible change of the blades in shape. In brief, the blades for the conventional centrifugal fan have the following disadvantages: (1) being limited in the structural design thereof; (2) providing only limited pressurizing effect; (3) having relatively poor air guiding efficiency; and (4) producing relatively high noise.